In order to extend our basic knowledge of the sensory perception systems in animals, and based on our previous demonstration that two migratory fishes have sufficient sensitivity to detect weak electric fields, we propose to give the hypothesis of electro-and magneto-orientation by fishes serious and detailed consideration. The specific objectives are to determine (1) a conditioned behavioral d.c. electric current sensitivity threshold, (2) electrosensitivity in actual migratory stages in the life cycle, (3) if the fishes can discriminate electric field polarity, (4) if the orientation of a weak d.c. electric field can influence the body orientation, (5) if the orientation of a weak d.c. magnetic field can influence body orientation, (6) the dorso-ventral sensitivity of the fishes to a weak d.c. electric field, and (7) the electrosensitive region of the body. Methods include conditioned cardiac deceleration, various conditioned avoidance and discrimination methods, automated body orientation recording techniques, and direction of turning experiments. Atlantic salmon (Salmo salar) and American eels (Anguilla rostrata) are the subject animals.